The present invention relates to multilamp photoflash units and, more particularly, to the efficient arrangement of photoflash lamps and reflectors in a planar array.
Numerous multilamp arrangements with various types of sequencing circuits have been described in the prior art; particularly, in the past few years. A currently marketed photoflash unit (described in U.S. Pat. Nos. 3,894,226; 3,912,442; 3,935,442; 3,937,946; 3,941,992; 3,952,320 and 4,017,728 and referred to as a flip flash) employs high-voltage type lamps adapted to be ignited sequentially by successively applied high-voltage firing pulses from a source such as a camera-shutter-actuated piezoelectric element. The flip flash unit comprises an elongated planar array of eight high-voltage type flashlamps mounted on a printed circuit board with an array of respectively associated reflectors disposed therebetween. The lamps are arranged in two groups of four disposed on the upper and lower halves respectively of the rectangular-shaped circuit board. A set of terminal contacts at the lower end of the unit is provided for activation of the upper group of lamps, while a set of terminal contacts at the top of the unit is operatively associated with the lower group of four lamps. The application of successive high-voltage pulses (e.g. 500 to 4,000 volts from, say, piezoelectric source controlled by the shutter of a camera in which the array is inserted) to the terminal contacts at the lower end of the unit causes the four lamps at the upper half of the array to be sequentially ignited. The array may then be turned end for end and again inserted into the camera in order to flash the remaining four lamps.
The flip flash circuit board comprises an insulating sheet of plastic having a pattern of conductive circuit traces, including the terminal contacts, on one side. The flashlamp leads are electrically connected to these circuit traces by means of eyelets secured to the circuit board and crimped to the lead wires. The circuitry on the board includes six printed, normally open, connect switches that chemically change from a high to lower resistance, so as to become electrically conducting after exposure to the radiant heat energy from an ignited flashlamp operatively associated therewith. The purpose of these switches is to provide lamp sequencing and one-at-a-time flashing. The four lamps of each group are arranged in parallel with three of the four lamps being connected in series with their respective thermal connect switches. Initially, only the first of the group of four lamps is connected directly to the voltage pulse source. When this first group flashes, it causes its associated thermal connected switch (which is series connected with the next or second lamp) to become permanently conductive. Because of this action, the second lamp of the group of four is connected to the pulse source. This sequence of events is repeated until all four lamps have been flashed.
The overall construction of the flip flash unit comprises front and back plastic housing members with interlocking means for providing a unitary structure. The front housing member is a rectangular concavity and the back housing is substantially flat. Sandwiched between the front and back housing members, in the order named, are the flashlamps, a unitary reflector member, preferably of aluminum-coated plastic, shaped to provide the eight individual reflectors of the array, an insulating sheet, the printed circuit board, and an indicia sheet, which is provided with information, trademarks, and flash indicators located behind the respective lamps and which change color due to heat and or light radiation from a flashing lamp, thus indicating at a glance which of the lamps have been flashed and not flashed.
The production of compact photoflash arrays, such as the flip flash described above, has forced lamp manufacturers to use stronger, hard glass vessels, such as those of borosilicate glass (e.g., see U.S. Pat. No. 3,506,385), to contain the higher internal loadings of oxygen and filamentary combustible material which are needed to provide a required light output in specific reflector embodiments, along with product safety. For example, in a present flip flash type unit containing lamps manufactured from borosilicate glass, the finished lacquer-coated lamp has a diameter of about 0.285 inch, a length of about 1 1/32 inches, and an internal volume of about 0.35 cc. Each lamp contains an oxygen fill pressure of 950 cm. Hg. (12.5 atmospheres) and a sufficient quantity of shredded zirconium, as the combustible metal fill, to obtain a specified light output when used in a prior art reflector, which is most efficient for this lamp size. This reflector has an aperture width of about 0.750 inch and a height of about one inch.
A substantial reduction in the cost of the aforementioned flip flash unit can be achieved by the use of lamps having envelopes formed of less expensive soft glass compositions. To maintain output and safety requirements, however, the envelope size of the soft glass lamp must be larger than that of the corresponding hard glass lamp. Copending application Ser. No. 823,794, filed Sept. 1, 1977, and assigned to the present assignee, describes an improved lamp reflector module which permits the use of larger soft glass lamps in a flip flash package having the same exterior dimensions as the previous hard glass type.
Even when using soft glass lamps, however, the cost per flash of a flip flash unit continues to be relatively high when compared to flashcube and magicube photoflash units. An approach toward further reducing the cost per flash is to provide additional soft glass lamps in the same package volume while maintaining performance requirements. A particularly convenient number of lamps for a flip flash unit would be ten, since many of the applicable types of film packs are provided with ten or twenty-frames. To arrange ten lamps and reflectors in a housing which had previously accommodated a compact planar array of eight lamps poses a significant problem.